Our aim is to characterize the cellular differentiation associated with premalignant changes in respiratory epithelium. This has been studied at the level of: A. Neuroendocrine differentiation. We have demonstrated that 15% of non small cell lung carcinomas (NSCLC) express multiple neuroendocrine (NE) features. Our results indicate that these tumors are sensitive to chemotherapy. The role of NE differentiation in nonneoplastic epithelium is investigated. B. Peripheral airway cell differentiation, We found 30% of the 400 NSCLC tumors examined to be positive for at least one of the peripheral airway cell (PAC) markers SP-A and CC-10. They also formed a clinically distinct subset. Characterization of NSCLC cell lines expressing PAC markers is in progress. In order to define premalignant lesions, we are studying the response of PACs to pulmonary carcinogens in nonneoplastic lung. C. Clara cell specific protein (CC-10). We have demonstrated that non-ciliated secretory cells, which are progenitor cells for the epithelium and NSCLC, express high levels of CC-10, while only 10% of NSCLC are positive for CC-10. Preliminary studies have shown that the levels of CC-10, also known as PCB (a potent carcinogen)-binding protein, are affected by exposure to carcinogens. To study the role of CC-10 in carcinogenesis, cloning of the human CC-10 gene regulatory region and functional analysis of the protein is in progress. D. Oncogene expression, We have found overexpression of c-myc in a high number of NSCLC as well as in the progenitor cells in human lung by in situ hybridization. The abnormalities of p53 tumor suppressor gene are currently being localized in the same material, since our results on lung cancer cell lines indicated that the p53 immunoreactivity in cells correlated with the mutations of the gene. The significance of the project is that the results will provide a rational basis for innovative approaches for early detection and intervention in human lung cancer.